The present invention is directed, in general, to electric meters and, more specifically, to an antenna for an electric meter to enable the meter to communicate over a public wireless data network, a method of manufacturing the antenna and an electric meter employing the antenna.
Until recently, a single utility provided electric service to all consumers in a given area. Establishment of electric service, maintenance, meter reading and billing were centralized in the single utility. Customers had no freedom to choose their electricity provider. Now, the kind of deregulation that changed the face of the telecommunications industry is sweeping through the electric power industry. One by one, states are allowing electric power resellers to buy electricity in quantity and to resell the electricity directly to consumers.
At the same time, electricity providers are becoming more sophisticated about billing practices. Gone are the days when consumers were billed flat rates. Numbered are the days that consumers are simply billed on the basis of kilowatt-hours consumed. Now, electricity providers are interested in gathering qualitative and additional quantitative data regarding electrical service delivered to consumers in an effort to correlate charges and costs of the service provided.
In response, consumers (particularly commercial consumers) are becoming more sophisticated regarding their use of electricity. Realizing that management of electrical usage may result in monetary savings, consumers are also demanding greater amounts of qualitative and quantitative data.
The electric meter industry has responded with digital electric meters that measure such characteristics as volt-hours, volt-squared-hours, watt-hours, kilowatt-hours, Qhours, VAR-hours and VA-hours over time, giving both the electricity provider and the consumer a greater quantity of, and more timely, data regarding electricity use. Examples of digital meters may be found in U.S. Pat. No. 4,884,021, issued Nov. 28, 1989, to Hammond, et al., entitled xe2x80x9cDigital Power Meteringxe2x80x9d and U.S. Pat. No. 5,122,735, issued Jun. 16, 1992, to Porter, et al., also entitled xe2x80x9cDigital Power Metering,xe2x80x9d commonly assigned with the present invention and incorporated herein by reference. Digital meters can measure these characteristics instantaneously or over a period of time, allowing electricity providers to track peak electricity usage and to better plan generator capacity. Electricity providers may then allow consumers to reduce costs by avoiding peak usage periods. Overall, digital meters have brought about more accurate measurement and billing and, in some cases, have resulted in more cost-effective use on the consumer""s part.
Like traditional mechanical meters, many digital meters must be read by direct visual observation. In large urban areas with millions of customers, this represents a considerable labor cost, even when spread out over an entire month. Additionally, meters have proven difficult to read from distances over 12 feet. Intervening fences, brush, trees, yard tools and pets may make close access difficult or even impossible. Sun glint and bad weather may add to the problem, particularly in remote areas with poor roads or during winter storms that may cover the meters with snow or ice. Ever-present is the risk that a meter reading may be erroneous. Deregulation of electric power may exacerbate this problem by creating geographically distributed electricity providers, thereby dramatically increasing the cost of reading meters and potentially threatening the economics of deregulation.
The electric meter industry has responded by adding wire-based communication circuitry to newer models of electric meters. Such circuitry typically employs a telephone line to communicate with a central location. While adequately addressing the cost issue of meter reading, the use of telephone lines introduces other problems.
If an electric meter is given a dedicated telephone line, the cost of the dedicated line must be considered when calculating the cost of reading the meter. On the other hand, if the electric meter shares a telephone line with another user (e.g., a residential meter may employ the residence""s main telephone line), the line may not be available when required by the meter. In fact, a consumer may intentionally make the line unavailable to the meter, thereby preventing the meter from reporting its data.
Alternatively, the meter may be provided with an external antenna to allow wireless communication over a range of a few hundred feet. A roving truck carrying a transceiver may then establish communication with the meter as it passes nearby, thus reading the meter. Unfortunately, the truck must be physically deployed to locations proximate the meters. Truck-based wireless reading, therefore, provides only a marginal advantage over direct visual observation. Further, the meter""s external antenna may be subject to tampering and to severe weather.
Accordingly, what is needed in the art is a more effective way to receive frequent, timely and accurate electrical consumption data from, and provide remote commands to, geographically-distributed electric meters.
To address the above-discussed deficiencies of the prior art, the present invention provides, for use with an electric meter chassis having a dielectric housing (of any geometry) protruding therefrom, an antenna for allowing electric meter circuitry within the chassis to communicate wirelessly through the dielectric housing and a method of manufacturing the same. In one embodiment, the antenna includes: (1) antenna elements, located within and generally conforming to a portion of an internal surface of the dielectric housing and adapted to transmit and receive electromagnetic radiation and (2) a balance circuit, coupled to the antenna elements to cause the antenna elements to act as a dipole and couplable to an unbalanced output port of a wireless communication circuit, that balances an impedance of the unbalanced output port thereby to balance the dipole.
The present invention therefore introduces the broad concept of outfitting an electric meter with an internal, wireless communications antenna, allowing the electric meter circuitry within the meter to communicate via a data network wirelessly couplable thereto. Such communication can be bidirectional, allowing the meter to report data to a central location or to accept remotely-generated operational commands. The range of the communications antenna is preferably sufficient to allow wireless communication with a data network, thereby eliminating a need to employ roving trucks to establish communication.
In one embodiment of the present invention, the antenna elements generally conform to a portion of an internal surface of the dielectric housing. If, as in an embodiment to be illustrated and described, the dielectric housing is cylindrical, the antenna elements can assume an arcuate form (or a straight form if conforming to an end of the housing).
In one embodiment of the present invention, the antenna further includes electric meter circuitry located in a circuit board rack within the dielectric housing, the antenna elements located between circuit boards in the circuit board rack. The electric meter circuitry, which is purely environmental with respect to the antenna embodiment of the present invention, may be distributed among separate, perhaps interconnected, circuit boards in the rack. Alternatively, the electric meter circuitry may be contained in another portion of the electric meter chassis.
In one embodiment of the present invention, the antenna further includes: (1) electric meter circuitry located in the dielectric housing and (2) an electromagnetic shield located about at least a portion of the electric meter circuitry. The electromagnetic shield, while not necessary to the present invention, can improve antenna performance by decreasing interference by reason of the proximity of the electric meter circuitry to the dipole.
In one embodiment of the present invention, the antenna elements are arcuate and have a flattened lateral cross section. Of course, other conductor shapes are fully within the broad scope of the present invention.
In one embodiment of the present invention, the balance circuit is embodied on a circuit board having mounts located thereon and mechanically supports the antenna elements, the mounts allowing the antenna to be reoriented with respect to the dielectric housing. The structure and operation of the mounts and the resulting flexibility in antenna orientation will be set forth in greater detail in the description of certain embodiments of the invention that follow.
In one embodiment of the present invention, the antenna elements are first and second conductors of a dipole and the balance circuit balances an impedance of the dipole. Those skilled in the art will recognize, however, that the antenna elements can form other types of antennas, such as single pole over ground plane, Yagi or loop antennas. Although the embodiment to be illustrated and described is directed to use of a dipole, the present invention is not so limited.
In one embodiment of the present invention, the antenna further includes a wireless communication circuit having a carrier frequency of between 700 and 950 megahertz, and, more particularly, between 806 to 825 (transmit) and 851 and 870 (receive) megahertz. Those skilled in the art will realize that this range of frequencies encompasses some well-known public data wireless networks, such as Ardis(copyright) or RAM Mobile Systems(copyright).
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.